Throw expressions

We also need to add the code to save a new storage space. Add the following code to the Click event of the btnSaveNewStorageSpace button:

private void btnSaveNewStorageSpace_Click(object sender,
  EventArgs e) 
  { 
    try 
    { 
        if (txtNewStorageSpaceName.Text.Length != 0) 
        { 
            string newName = txtNewStorageSpaceName.Text; 
 
            // throw expressions: bool spaceExists = 
           (space exists = false) ? return false : throw exception                     
            // Out variables 
            bool spaceExists = (!spaces.StorageSpaceExists
            (newName, out int nextID)) ? false : throw new 
            Exception("The storage space you are 
             trying to add already exists."); 
 
            if (!spaceExists) 
            { 
                StorageSpace newSpace = new StorageSpace(); 
                newSpace.Name = newName; 
                newSpace.ID = nextID; 
                newSpace.Description = 
                txtStorageSpaceDescription.Text; 
                spaces.Add(newSpace); 
                PopulateStorageSpacesList(); 
                // Save new Storage Space Name 
                txtNewStorageSpaceName.Clear(); 
                txtNewStorageSpaceName.Visible = false; 
                lblStorageSpaceDescription.Visible = false; 
                txtStorageSpaceDescription.ReadOnly = true; 
                txtStorageSpaceDescription.Clear(); 
                btnSaveNewStorageSpace.Visible = false; 
                btnCancelNewStorageSpaceSave.Visible = false; 
                dlVirtualStorageSpaces.Enabled = true; 
                btnAddNewStorageSpace.Enabled = true; 
            } 
        } 
    } 
    catch (Exception ex) 
    { 
        txtNewStorageSpaceName.SelectAll(); 
        MessageBox.Show(ex.Message); 
    } 
} 

Here, we can see another new feature in the C# 7 language called throw expressions. This gives developers the ability to throw exceptions from expressions. The code in question is this code:

bool spaceExists = (!spaces.StorageSpaceExists(newName, out int nextID)) ? false : throw new Exception("The storage space you are trying to add already exists."); 

I always like to remember the structure of the code as follows:

The last few methods deal with saving eBooks in the selected Virtual Storage Space. Modify the Click event of the btnAddBookToStorageSpace button. This code also contains a throw expression. If you haven't selected a storage space from the combo box, a new exception is thrown:

private void btnAddeBookToStorageSpace_Click(object sender, EventArgs e) 
{ 
    try 
    { 
        int selectedStorageSpaceID = 
         dlVirtualStorageSpaces.SelectedValue.ToString().ToInt(); 
        if ((selectedStorageSpaceID !=   
         (int)StorageSpaceSelection.NoSelection) 
        && (selectedStorageSpaceID !=
          (int)StorageSpaceSelection.New)) 
        { 
            UpdateStorageSpaceBooks(selectedStorageSpaceID); 
        } 
        else throw new Exception("Please select a Storage 
       Space to add your eBook to"); // throw expressions 
    } 
    catch (Exception ex) 
    { 
        MessageBox.Show(ex.Message); 
    } 
} 

Developers can now immediately throw exceptions in code right there where they occur. This is rather nice and makes code cleaner and its intent clearer.